Improved flooring



Dec. 26, 1939. R, McD. FREER El AL 2,184,811

IMPROVED FLOORING Filed May 10, 1938 gwwm/fms RobertUl/cDamldH-eer G'eorf'ellon ia fl im Patented Dec. 26, 1939 HWPROVED FLOORING Robert McDonald Freer, Saltcoats, and George Morris, Ardrossan, Scotland, assignors to Imperial Chemical Industries Limited, a oorporation of Great Britain Appiication-May 10. 1938, Serial No. 207,100 In Great Britain May 13, 1937 7 Claims.

The present invention deals with the manufacture of floors for buildings, especially floors characterised by a relatively good electrical conductivity.

In many industrial operations, such as flourmilling, grinding of various materials, transference of fluids through pipes and nozzles, and other processes involving at some stage a frictional contact of dissimilar materials, frictional or static electricity is generated; and in favourable circumstances the materials may accumulate a static charge of such magnitude that the approach of a conductor will cause a spark discharge. In many of the industrial operations under consideration the working conditions are such that a spark discharge may have serious consequences; for instance, violent dust explosions have been caused in flour mills by such means, and fires have been caused by spark, discharges during the transference of inflammable liquids through nozzles. It is accordingly highly desirable that static charges should not be allowed to accumulate at any point during these processes; and that, if their formation cannot be altogether prevented, they should be dissipated before a dangerous voltage can be generated.

The customary precautions to this end consist in the provision .of an earthing system whereby all conductors from which a discharge may take place are electrically bonded together and .connected to earth; and of earthed collectors at points, such as belt drives or dust chutes, where experience has shown that static electricity is most readily generated. Such methods, however, although satisfactory when applied to fixed machinery are not readily applicable to moving objects, such as trolleys, barrows and even workmen themselves, that may carry static charges from place to place. The method adopted hitherto for dealing with such objects has been the provision of metallic floors, or of floors in which the surface is kept in a sufliciently conductive state by being flooded with water or by the use of hygroscopic materials.

In certain manufactures however, these latter methods are not generally admissible; in the manufacture of explosives, for instance, metallic floors may be dangerous on account of sparks caused mechanically by falling objects, or the formation of explosive compounds by chemical action; and wet and slippery floors may interfere with processes carried out under controlled humidity conditions and endanger the workers themselves. Furthermore, metallic floors readily form non-conductive surface coatings, and must be frequently cleaned if their conductivity is to be relied on for the purpose in view.

This invention has as an object to provide flooring which will combine good and permanent electrical conductivity with a strong surface and freedom from the danger of mechanical sparking and chemical action. A further object is to provide flooring which will have the above advantages when dry. A still further object is to devise methods of manufacturing such flooring. Further objects will appear hereinafter. These objects are accomplished by the following in vention;

We have found that we can make a flooring which achieves these objects if we lay a flooring material, made by mixing ground coke with a bituminous material of the type commonly eme ployed for mastic floorings, on an earthed metallic strip or network.

According to the present invention, therefore,

an electrically conductive flooring composition comprises a mixture of ground coke and a bituminous binder in electrical contact with an earthed conductor. In the accompanying drawing, Figure 1 represents a vertical section through a floor made according to this invention. Figures 2, 3 and 4 illustrate three difierent methods of laying the earthed conductor.

Referring to Figure l, l is a concrete bed on which the flooring is based; 2 is the earthed conductor which runs nearly the whole breadth of the floor as shown in Figure 3; 3 is one of the metal cross-strips somewhat shorter than the length of the floor which are laid at intervals along the floor so as to make a good electrical contact with the earthed conductor 2 at the point where they cross. The metal cross-strips are also shown and marked 3 in Figure 3. 4 is the layer of bitumen and ground coke.

Figure 2 shows the layout of the earthed conductor that has been found suitable for a room 16 feet by 28 .feet. 5 represents a plan view of the floor, the conductor. being marked 6 and running almost peripherally. around the floor. 2 represents the lead out from the conductor 6 to the earth at E.

'Figure 3 shows a layout suitable for larger floors. 5 again represents the plan view of the floor. The conductor 2 runs from the earth E nearly the whole breadth of the floor while crossstrips 3 are laid so that they reach nearly to the ends of the floor.

Figure 4 shows another form of layout. In this case the conductor 2 runs diagonally across the door reaching from one corner-to near the opposite corner. A cross piece 3 in electrical contact with 2 runs across the other diagonal.

The following example illustrates the invention.

Example A composition is made comprising ground gas coke (47% by weight) mixed with ground foundry coke (23.5%) and Trinidad asphalt cement (29.5%). The penetrometer test of the asphalt is units at 77 F. Theresistivity of the materlal is 2,500 ohms per centimeter cube. The earthed conductor consists of a copper tape broad by $4, thick pegged down flat on a concrete floor and connected to a suitable earth. The composition is laid in contact with the tape to a uniform depth of 54;". The resistance of the finished floor to earth does not at any point exceed 4,000 ohms.

The penetrometer test referred to above is described in The Institute of Petroleum Technologists Handbook, 3rd edition, 1935, Serial Method A. 18.

For binder we prefer to use an unfilled asphaltic bitumen but any other binder which is commonly used for mastic flooring can be used.

The metal strip' used can be of any gauge or weight that has not too high a resistance and the method of spacing the metal strips and, where used, the cross-strips, will depend partly on this and partly on the thickness and general conductivity of the coke-bitumen mixture. For most purposes the floor is sufllciently conductive if the resistance from any point on it to earth is less than 21.7 megohms. In practice we prefer to keep below 3 megohms. A skilled worker knowing the conductivity of the coke bitumen mixture that he is using and of the metallic strip could from these figures calculate the spacing of the conductor.

The strip can either be laid on the concrete floor and the conductive material rolled over it or a layer of the conductive material could be laid first and another layer on top of the strip so as to embed the strip in the conductive material.

The coke used is preferably a high temperature coke from high grade coal and is suitably ground to 12-16 mesh. As diiferent samples of coke may vary considerably in their electricalconductivity, it is advisable to make a rough test of theconductivity of the crushed coke between electrodes in order to select the most suitable material.

The most suitable proportions for the mixture are about 30-35% asphaltic bitumen and 70-65% ground coke, but proportions of coke as high as 75-80% or as low as 60% can be used. Variations in composition may be made according to the fluidity of the bitumen used, but the final composition should preferably have a penetrometer test in the neighbourhood of 10 units.

Besides being electrically conductive, the flooring mixture of the present invention can be softened or melted, poured and smoothed by the methods commonly employed in laying mastic 1100111188, or by obvious modifications thereof. moors constructed therewith are free from dust,

non-slipping, hand-wearing, and chemically inart, and they retain their conductivity permanently. These floorings are thus especially adapted for use in buildings in which dangerous operations. such as the manufacture or handling of explosives or combustibles, are carried out.

As many apparently widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof, except as defined in the appended claims.

y We claim:

1. An electrically conductive flooring composition comprising a mixture of ground coke and a bituminous binder having an electrical resistivity not exceeding2500 ohms per centimeter cube.

2. An electrically conductive flooring composition comprising a mixture of 80-60% of ground coke and 20-40% of bituminous binder.

3. An electrically conductive flooring composition comprising a mixture of 30-35% asphaltic bitumen and 70-65% ground coke. 4. A floor comprising, in combination, an electrically conductive flooring composition comprising a mixture of ground coke and a bituminous binder, and an earthed metallic conductor in electrical contact with said composition.

5. A floor comprising in combination an electrically conductive flooring composition comprising a mixture of ground coke and a bituminous binder, and an earthed metallic conductor in electrical contact with said composition, said conductor being shielded from. contact at the floor surface and so placed that the resistance to earth from any point on the floor surface is less than 21.7 megohms.

6. A floor comprising in combination an electrically conductive flooring composition comprising a mixture of ground coke and a bituminous binder having an electrical resistivity not exceeding 2500 ohms per centimeter cube, and an earthed metallic conductor in electrical contact with said composition, said conductor being shielded from contact at the floor surface and so placed that the resistance to earth from any point on the surface is less than 21.7 megohms.

7. A floor comprising in combination an electrically conductive flooring composition comprising, anmixture of ground-coke and a bituminous binder containing 20-40% of the binder and 8060% of the ground coke, and an earthed metallic conductor in electrical contact with said composition, said conductor being shielded from contact at the floor surface and so placed that the resistance to earth from any point on the surface is less than 21.7 megohms.

ROBERT MCDONALD FREER. GEORGE MORRIS. 

